This invention relates to a process for the production of a polybutene-1 formable into transparent sheets and heat sealable films, and to the polybutene-1 thus produced and films formed therefrom.
Films of highly isotactic polybutene-1 produced in a conventional manner, e.g., U.S. Pat. Nos. 2,909,511; 3,051,690; 3,058,963; 3,058,980; 3,108,973; 3,362,940; British Pat. No. 1,017,848; and Rust, et al., "Crystalline Olefin Polymers", Part I, Interscience Pub. N.Y. (1965) pp 333-334; have the disadvantage that they exhibit not only low transparency but also widely differing tensile strength in the longitudinal and transverse directions, and consequently a poor resistance to tear propagation (film tear strength). Therefore, films from such high-isotactic polybutene-1 are not suitable for many fields of application.
By increasing the atactic proportion of such polybutene-1 polymers, the transparency of such films formed therefrom can be improved only slightly. For example, if the atactic proportion is not separated together with the solvent during the working-up step following polymerization, but instead is left in the product by precipitation of the total polymeric product with alcohol or by evaporation of the polymerization solvent, a polybutene-1 is obtained whose films show only a small improvement in transparency, even in the case of polymer products containing 10-20% ether-soluble (atactic) proportions. Moreover, the resistance to continued tearing is not improved compared to films formed from the highly isotactic polybutene-1 and differs widely in the longitudinal and transverse directions, e.g., 24.8 kp./mm. in the longitudinal direction and 0.89 kp./mm. in the transverse direction.
U.S. Pat. No. 3,468,862 discloses a method of improving the transparency of films of conventional polybutene-1 polymers but that method, since it involves biaxial stretching, produces films which cannot be satisfactorily heat sealed.
Since heat sealable transparent films having the other excellent properties of polybutene-1 would be desirable, there is a need for a commercially feasible process for the production of a polybutene-1 from which transparent films can be formed which have satisfactory resistance to tear propagation.
For illustrative prior art relating to the polymerization of olefins, see U.S. Pat. No. 2,909,511; 3,051,690; 3,058,963; 3,058,970; 3,362,940; 3,108,973; 3,385,817; 3,468,862, and British Pat. No. 1,017,848. U.S. Pat. No. 3,108,973 employs a catalyst which contains AlRCl.sub.2 and does not produce a polybutene having the properties of the polybutene of this invention. U.S. Pat. No. 3,058,970 is a broad teaching of suspensions polymerizations of 1-olefins in inert solvents. U.S. Pat. No. 3,051,690 broadly describes solution polymerizations in n-heptane. U.S. Pat. No. 3,058,963 is a more specific teaching within the broad teaching of 3,058,970. U.S. Pat. Nos. 2,909,511, 3,362,940 and British Pat. No. 1,017,848 describe polybutenes differing from those of this invention. U.S. Pat. No. 3,468,862 discloses a process for increasing the clarity of films.